Many applications in modern electronics require that continuous-time signals be converted to discrete-time signals for processing using digital computers and signal processors. Typically, this conversion is made using a sampler/quantizer circuit that, at each of a sequence of uniform time intervals, rounds the value of a continuous-time, continuously-variable analog signal into one of a finite number of discrete values. This rounding operation typically is performed through the use of one or more voltage comparators, such as comparators 12-14 in the exemplary, conventional two-bit sampling circuit 10 illustrated in FIG. 1. Exemplary sampling circuit 10 sometimes is referred to as a Flash converter in the prior-art literature. Referring to FIG. 1, a resistor ladder (including equal-valued resistors 16 and 17) establish three uniformly spaced voltage thresholds 21-23 VT+, (VT++VT−)/2 and VT−, which are compared against the analog input signal voltage 30 in the three comparators 12-14 at each point in time identified by sampling signal 32. For a low input voltage, all three comparator outputs get latched in a low state, represented by a binary thermometer code of ‘000’. For a high input voltage, all three comparator outputs get latched in a high state, represented by a binary thermometer code of ‘111’. Therefore, the four possible thermometer codes that represent the four possible input voltage states are: ‘000’, ‘001’, ‘011’, and ‘111’. The first (leftmost) bit in the thermometer code is determined by comparator 12, the second (middle) bit in the thermometer code is determined by comparator 13, and the third (rightmost) bit in the thermometer code is determined by comparator 14. A logic decoder 35 then converts each of the four possible thermometer codes into one of four binary (e.g., two's complement) values: ‘10’, ‘11’, ‘00’, and ‘01’. In such a two-bit binary representation of an analog signal that is expected to vary between |Vmax| and −|Vmax|, the first bit, or most significant bit (MSB), represents the sign of the analog signal; and the second bit, or least significant bit (LSB), represents the magnitude of the analog input signal.
While the conventional two-bit quantizing circuit is useful for its intended purpose, the present inventor has discovered that a reduced-complexity circuit can be implemented.